An implant is a medical device manufactured to replace and act as a cover to a missing biological structure or to fit a pathological area of human body. Most of the implants are made up of biocompatible materials such as titanium, ceramic and others depending on what is the most functional. Medical implants are usually applied in the orthopaedic, cranioplasty, neurosurgery, oral surgery, plastic surgery and other pathological fields to repair or recontour a defect at a particular pathological area of a patient. Generally, a custom made medical implant will be an advantage considering the compatibility and precision of the implant to a patient's pathological area.
Conventionally, medical implant is shaped to a patient's pathological area at the time of surgery. Majority of medical doctors and surgeons rely only on two-dimensional (2D)-based medical images for diagnosis, treatment and surgery. These 2D based images, especially Computer Tomography (CT) and Magnetic Resonance Imaging (MRI) are generated by the medical scanners and often viewed directly from a computer terminal or printed out on film. The knowledge and experience to understanding and interpretation of these 2D images take many years of practice and intuitive thinking. In some cases, even an experienced doctor or surgeon will face great difficulty in understanding and making the right diagnosis, especially in complicated cases.
The difficulty in grasping 2D images arises when a medical practitioner has to review multiple 2D images in order to understand the precise anatomy or morphology of a three-dimensional (3D) object, such as a bone or tumor. The multiple 2D images are reconstructed in mind and conceptually converted to virtual 3D images. When carrying out a surgery, the medical practitioner will have to rely on the 2D images to map out the correct path to repair a defect without harming any other healthy parts of a patient's anatomy. This phenomenon is especially significant in the area of maxillofacial reconstruction where surgeons depend on simple measurements according to 2D images of a bony structure which are then translated into 3D object during surgery. The implants are retro-fitted onto the patient during surgery so as to fit the pathologically defective or anatomically deformed area. These approaches often result in the patient exhibiting slight deformities due to the misjudgment when forming the implants manually, which requires further surgery to repair or recontour.
Since most surgeons fixing a defect at a pathologically defective or anatomically deformed area of a patient by retro-fitting an implant at the time of surgery and with the patient's anatomy exposed, a lot of difficulties arises. These include longer surgery time, higher risk of infection and/or aesthetically unpleasing results. Therefore, some implants may have to be constructed before the surgery. In recent years, various groups around the world have been working on the design and fabrication of customized medical implants.
There are a few inventions described by the prior arts relating to a method for producing medical implants or reconstruction and the product thereof. These patented technologies include a wide variation in their manufacturing methods and qualities of the products.
Of interest in connection with a method for designing and producing a custom-fit prosthesis is U.S. Patent No. US2005133955. According to the preferred embodiment of this prior art, a mould is produced and from which a custom-fit implant may be directly or indirectly manufactured. The method described in this invention comprises the steps of receiving medical image data representing surrounding portions of a patient's anatomy to be repaired, performing 3D surface reconstruction, designing a custom-fit implant, modelling a two-part mould with a void in the shape of a custom-fit implant and outputting the two-part mould from which the custom-fit implant may be manufactured. This method focuses mainly on the manufacturing method of the mould and it is usually applied in cranioplasty.
Of interest in respect to a method for contouring bone reconstruction plates is U.S. Pat. No. 6,978,188. This invention discloses a method of producing a template for use in pre-contouring bone reconstruction plates, wherein the method comprises the steps of receiving medical image data representing surrounding portions of a patient's anatomy to be repaired, performing 3D surface reconstruction, performing virtual removal of a bony structure to be reconstructed with reference to the medical image data by stimulating the surgical implantation procedure; creating a representation of a template contoured to fit a patient's anatomy to be repaired; and outputting a replica of the template buy using Solid Free-form Fabrication manufacturing techniques. However, the recontouring process of implant is carried out at the time of surgery.
Another U.S. Patent No. US2004102866 also relates to surgical planning methods and in particular to the planning of surgical operations to implant a prosthesis. The invention uses an interactive system to design both the shape of the prosthesis and the shape of the bone. In another embodiment, a modified Marching Cubes algorithm is used to simulate cutting planes within bones. Besides, a back-projection used within a computer model to allow an integrated display of both bone and prosthesis and an interactive system used to test the mobility of a proposed implant are also embodied in this prior art. This prosthesis invented is specifically applied to knee joint.
There is also a Germany Patent No. DE3933459 relating to a biomedical implant production equipment which uses computer tomographic image to generate an implant profile for component. The complete process is based upon five different steps. The primary data are provided by a computer tomographic image and a computer is used to post process the data into a form usable by a machine tool. This invention uses a laser cutter or milling machine for the manufacture.
Another Germany Patent No. DE19901271 also relates to an implant for reconstruction of (especially cranial) bone defects comprising aluminium oxide and zirconium oxide ceramic coated with tricalcium phosphate or hydroxylapatite for good biocompatibility. The method includes inserting an implant or a mould for casting an implant into a bone defective area. The implant is prepared by using an imaging process and is coated before the insertion.
There is also a method for generating patient-specific implants disclosed by Canada Patent No. CA2373691. This invention utilizes the medical image data of a patient to generate an implant which is functionally and aesthetically adapted to the patient with a greater degree of precision. According to this invention, a virtual 3D data of a patient is compared with real medical reference data. This data bank is used as reference to create an implant.
There is no patented technology over the prior arts disclosing a method for designing and manufacturing a custom-fit medical implant based on medical scan images of a patient's pathologically defective or anatomically deformed area where the implant designed will undergo refinement to reach a high degree in its precision. Since suitably fitting implants considerably improve the health and quality of life for a patient, the development, design and fabrication of a custom made implant is essential as it provides high degree of precision to the patient's anatomy.